Human locomotion, such as walking and running, is commonly described in terms of gait. Gait is a cyclical pattern of leg and foot movement that creates locomotion. A gait cycle is defined for a single leg and begins with the initial contact of the foot with the ground or heel strike. The conclusion of a gait cycle occurs when the same foot makes a second heel strike. The gait cycle can be divided into two phases, stance phase and swing phase. Stance phase begins with heel strike and ends when the toe of the same foot leaves the ground. Swing phase begins when the foot leaves contact with the ground and ends with the heel strike of the same foot.
Prosthetic and orthotic devices help restore mobility to people who lack able-bodied motion or gait. Prosthetic devices are intended to replace the function or appearance of a missing limb and can return mobility to the wearer or user. Orthotic devices are intended to support or supplement an existing limb, by assisting with movement, reducing weight-bearing loads on the body, reducing pain, and controlling or restricting movement. Prosthetic and orthotic devices are available to replace or support various portions of the body. Lower limb prosthetic devices include, for example, the prosthetic foot, the foot-ankle prosthesis, the prosthetic knee joint, and the prosthetic hip joint. Lower limb orthotic devices include, for example, the foot orthoses, the ankle-foot orthoses, the knee-ankle-foot orthoses, and the knee orthoses. People who require a lower limb prosthesis or orthosis often expend more metabolic power to walk or move at the same speed as able-bodied individuals. One goal of lower limb prosthetic and orthotic devices is to help the user achieve a normal gait while reducing energy expended by the user.
Prosthetic and orthotic devices can be divided into two groups, passive devices and active devices. Passive lower limb prosthetics generally rely on compliant members, such as springs, to store and release energy. A spring is able to return only as much energy as is put into the spring. Thus, the energy that is released by a spring in a passive device is limited to the energy that is put in by the user. For example, a spring-based passive foot prosthetic provides about half of the peak power required for gait. The user of a passive device must expend additional energy through other muscles and joints to maintain a normal walking gait. Therefore, passive prosthetic and orthotic designs are limited in capacity to help users reduce metabolic energy expenditure while achieving a normal walking gait and performing other activities.
Active devices differ from passive devices in that active devices use a motor to supply power to the device and to control the device. Control systems for active devices are limited in capability to control active devices during gait or other activities. Further, active prosthetics are limited to low power activities, because the power necessary for high power activities is unattainable in a small portable system. One goal of active device designs is to increase efficiency of the active components and to build a lighter weight device.
Control systems and methods designed for prosthetic, orthotic, and robotic gait devices to control motors for active devices. One current control algorithms for wearable robotic devices use a fixed pattern designed for a specific gait pattern, such as a specific walking speed. The fixed pattern algorithms must be modified for different gait patterns or activities. Therefore, a fixed pattern algorithm is limited to a single gait speed, while a user desires to walk or run at varying speeds. Other current control algorithms for wearable robotic devices use if-then logic, estimations of gait events, or decision making algorithms to determine the phase of a user's gait cycle. Decision making and state transition algorithms are known to be error prone, often resulting in undesirable operation when a state or phase of gait is chosen incorrectly.